Photoflash unit



May 9, 1961 R. s. JAMES ETAL PHOTOFLASH UNIT 4 Sheets-Sheet 1 Filed May l2, 1958 Maly 9, 1961 Filed Ma 12, 1958 4 Sheets-Sheet 2 25 l mm INVENTOR.

Robert S. .James BY F g. 2.

C ATTO@ May 9, 1961 R. s. JAMES ETAL 2,983,810

PHOTOFLASH UNIT Filed May l2, 1958 4 Sheets-Sheet 3 IN V EN TOR.

Robert S. James Y BY w J. Semon 2% May 9, 1961 R. s. JAMES ETAL PHOTOFLASH UNIT 4 Sheets-Sheet 4 Filed May 12, 1958 w w O O 5 w P 1 ,Q C/ C2 2 Q om,

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Fig. 8.

IN V EN TOR.

Robert S. James N S P. J. 0 A

e s 0 J W 2,983,810 PHTL-I UNF I-li Robert S. James and Joseph J. Sem'an, Pittsburgh, Pa.,

assignors to the United States'of America as represented by the Secretary of the Interior frire invention herein describen and claimed may be manufactured or used by or for the United States of Americaf for governmental purposes without payment of royalty thereon or therefor.

ThisV invention relates to a photoash `unit which is safe to use in areas likely to contain explosive gas or dust mixtures, such as coal mines, flour mills, chemical plants, Et. i

In the past, photoflash units have been constructed wherein internal parts are exposed to the surrounding atmosphere. Units so constructed when used in an explosive atmosphere might, because of arcing, sparks, or the explosion of the flash bulb, ignite the surrounding explosive atmosphere, with the result that an explosion could occur.

It is the Vprincipal object of 'the present invention to provide a photofl'ash unit which 'will not operate unless all `parts of the unit which may ignite an explosive at= mosphere are enclosed in an explosion-proof case.

It is a further object of the invention to provide an automatic circuit-controlling device, responsive to impairment of the explosion-proof feature of the case, which i United States Patent G l will deenergize the hazardous components of the circuit in the unit and permit spent flash bulbs to be removed in explosive atmospheres.

It is a further object of this invention to provide an explosion-proof photoflash lamp wherein the bulb is ignited by a circuit including a capacitance and wherein the bulb is removed from the circuit and the capacitance deenergized by having a resistance shunted across it when the device is no longer explosion-proof.

Further objects will be apparent from the following description of the invention.

The present device, which eliminates this danger, comprises a socket holding a photoflash bulb Within a `cylindrical ilametighthousing', one end of which is provided with a light permeable window removably mounted therein and sealed by suitably gasketed rrings. The socket and bulb assembly is removable from the housing through an access casing located at the side of the housing socket. Safety switches are provided in circuit with an electronic ring arrangement, so that when the bulb socket is moved from a predetermined position, the device is rendered inoperative. By this means, a fired bulb may be removed with complete safety in an explosive atmosphere, and any variation from a completely sealed condition render the electrical circuit inoperative.

Explosion-proof, as used herein, means .that those parts of the unit which may ignite an explosive atmosphere are enclosed in a case capable of withstanding gas explosions which might possibly occur therein, without damage to the case or ignition of explosive atmospheres surrounding the case. The Bureau of Mines requirements for explosion-proof lighting fixtures Jare set forth in Title 30, Code of the Federal Regulations and Bureau of Mines Schedule 29.

In the drawing:

Figure 1 is a vertical view, partly in section, of the 2,983,810 v Patented May 9,

device, some of the electrical wiring being omitted for' the sake of clarity'.

Figure 2 is a vertical view partly in section'taken ralong line 2-2 of Figure 1, the flash bulb and 'reector being omitted.

Figure 3 is a view taken along line 3-3 of Figre 1.

Figure 4 is a sectional View through the stuffing box.

Figuresl 5 and 6 are diagrammatic, exaggerated views showing the microswitch in open and closed positions respectively.

Figure 7 is a circuit diagram of the firing circuit showing the microswitches open.

Figure 8 is the same as Figure 7, but with the switches closed. Y Y

Cylindrical housing 1 is shown in vFigure 1 as having a tubular access portion 2 fastened thereto, and a backplate 3. Housing 1 at the end opposite backplate 3 is threaded internally to receive externally threaded rings 20 and 21. Nonflammable gaskets 22 abut against rings 20 and 21 and act to 'maintain a lens 23 between them, in a ametight seal. The assembly of lens 23, gasket 22, and rings 20 and 21 are secured against displacement by seal 24, fastened by wire 26 passing through holes in outer ring 20 and tie post 25 at the bottom of housing 1.

Fastened to 1 at opposite ends of a horizontal diameter, as shown in Figure 2, are -two yoke pivot bosses 4, each having a tapped hole at its central portion 'and a cylindrical portion of smaller diameter 5. Yoke 6 has circular apertures 7 in each of its upright arms into which members 5 fit. Screw 8 is threaded into boss 4 and has a rod 9 passing through its head for increased leverage in tightening. A friction washer 10 aids in main'- taining the desired angle of detiection of the housing. At the center of the bottom of the yoke is fastened tripod mount 11, by means of nut 12 and lock washer 13,l adapted to be attached to any conventional photographic tripod. Thumbscrew 14 aids in attaching the mount t'o its support.

Located at the top portion of housing 1 and fastened thereto is boss 15. Stem 16, which has a spherical ball 17 at its upper portion, is rigidly fastened to 15 in an upright position. Clamp 18 iits over ball 17 and holds photoelectric cell structure P in its upper jaws, pressure being applied by thumbscrew 19.

A stuffing box 27 (see Figure 4) extending through the backplate 3, receives two conductor cables 28, packing material 29, which lmay be asbestos, an'd externally threaded gland nut 30. The combination of the packing material 29, compressed by gland nut 30, and stutlng box 27, forms a flametight entrance for cable 28 to the interior of housing 1. Clamp 31 straddles condlgl'ct'or 28 and is drawn up tight by two screws 32, one on eith'eiside of the conductor, which' are threaded into gland 'nut Lock washer 33 prevents displacement of gland nut Tubular access portion 2 is threaded internally to receive an externally threaded cover 34 having a shoulder portion 35. When shoulder 35 is screwed tight against 2 this portion of the device is flametight. The arrangement described to this point, i.e., housing 1, tubular access portion 2, cover 34, stuiiing box 27, gland nut 30, packing material 29, rings 20 and 21, gasket 22, and lens 23, all combine together to form ailametight 'explosionproof case for the unit.

Fastened to the internal `surface of housing 1 are three bosses 36 spaced equidistantly around the circumference. Ring 37 is fastened to bosses 36 as by bolts '63 and clamps 69, and serves as the supporting .member for reflector 33. Two battery 'cases 39 located `near the cylindrical surface, are attached to ring 37 by means lof bracket 40 fastened to the housing. Mounting board 41, of an insulating material such as Bakelite, is attached to bracket 40 vand is the supporting means for lthe various tiring circuit components indicated in Figure 2. A strap -42 is fastened to board 41 to hold thyratron tube T.

Switch supporting bracket 43 is secured to bracket 40, and has connected to it an arm 44, which may be adjustably positioned thereon by screws 45 and slot 46. 'Two normally closed, single pole, double throw microswitches 47 and 48, having conducting blades 64 and 65 .are mounted on arm 44.

Lamp socket 49, made of heat resistant insulation material such as porcelain, ts into a sleeve 50 which has a pair of holes 51 near its base. Sleeve 50 fits into a recessed portion of cover 34, as shown in Figure 1. At the upper end of the sleeve is a ring 52, made of an insulating material, e.g., fiber, which serves to space the upper shoulder portion of socket 49 from sleeve 50.

Female threaded metal socket element 53 iits inside lamp socket 49 and receives the threaded base portion 54 of photoash bulb 55. The assembly of elements 49, 50, and 53 is firmly secured to cover member 34 by machine screw 56, the head of which lits into a circular recess at the bottom of 49. The bottom of base portion 54 bears against an electrical contact 57 connected to terminal screw 58 mounted in the bottom of socket 49, While female socket element 53 is electrically connected to terminal screw 59. Copper contacts 60 and 61 (see Figure 3) are mounted tiush with the upper surface of ring 52 and fastened thereto by means of a screw and nut, connected to terminal screws 58 and 59 by conducting wires 62 and 63. Conducting blades 64 and 65 are directly above contacts 60 and 61. When shoulder 35 is seated firmly against 2, blades 64 and 65 are in contact with 60 and' 61, and the switches are in their open position. Contrariwise, when the shoulder is not seated i'irmly, the lamp assembly then not being ametight and liameproof, blades 64 and 65 do not contact 60 and 61, and the circuit to the flash bulb is broken. Further outward movement of ring 52 causes switches 47 and 43 to return to their normally closed position, the circuit then .being as shown in Figure 8, as will be explained hereinafter.

The tiring circuit is shown in Figure 7. Condenser C1 charges through ash bulb 55 and resistor R4. When the capacitor is fully charged, a beam of light falling on photoelectric cell P will cause Thyratron tube T, which acts as a ring switch, to become conducting. The energy in condenser C1 then discharges through ash bulb 55, causing the latter to fire. The figure is believed to be self-explanatory to those skilled in the art and need not be described further. Suitable values for the various circuit components are as follows:

Resistors, ohms: R1=l0K; R2 and R3=22M; R4=62K; Condensers: C1=40 mfd.; C2=.005 mfd.; C3=0.25 mfd.; Batteries: E1 and E2=60 v.

Thyratron tube T is an IC-2l and photoelectric cell P is a CE-B6-C.

The operation of the device is as follows:

When cover 34 is slightly `displaced from its fiametight position in relationship to access member 2, as shown in Figure l, ring 52 will rotate and move outwardly. This rotation displaces contacts 60 and 61 on ring 52 from the conducting blades 64 and 65 of switches 47 and 48. The circuit to the flash bulb 55 is then broken. Continued outward movement of ring 52 causes switches 47 and 48 to return to their normally closed positions, thereby placing resistor R1 across capacitor C1 in the circuit as shown in Figures 6 and 8, and draining it. The condition of the circuit after capacitor C1 is discharged may be defined as intrinsically safe. As used herein, intrinsically safe means that those components remaining in circuit after capacitor C1 is discharged are incapable of forming arcs or sparks of sufficient intensity to ignite a surrounding explosive atmosphere.

After-:the circuit has beenrendered inoperative by a slight displacement at cover 34 from its flametight position, the cover may be completely unscrewed and the flash bulb 55 removed.

Connectors 66 and 67 provided on cable 28 facilitate the operation of the unit by providing a simple means for operating the unit photoelectrically, manually, or in synchronization with a suitable camera shutter mechanism. To operate the unit photoelectrically, the photocell P is connected as shown in Figures l and 7. Light falling on photocell P will cause thyratron T to become conducting. Capacitor C1, previously charged by current through R4, will then discharge through thyratron T and flash bulb 55. For manual operation, connectors 66 and 67 are separated, thereby disconnecting the photoelectric .cell P from the circuit. A mostened finger is then placed across the terminals of connector 66, causing capacitor C1 to discharge. For operation in syn- .chronization with a camera shutter mechanism ,the latter is connected to 66 by an electrical conductor.

The current ilowing in cable 28 never exceeds more than several microamperes, and is incapable of forming arcs or sparks, which can ignite an explosive atmosphere. Thus, connectors 66 and 67 may be disconnected in an .explosive atmosphere without constituting explosion hazards, thereby permitting the unit to be manually operated as a primary light source for several similar units operated photoelectrically.

It is apparent that various modifications may be made in the design of the housing and the firing circuit without altering the essential features of this invention.

We claim:

1. An explosion-proof phototiash unit comprising a photoash bulb having the usual threaded base portion and electrical terminals, a ametight housing surrounding said ash bulb including transparent window means, an access tube having inner and outer end portions connected to said housing at said inner end, retractable cover means mounted in said access tube adapted to form a ametight seal, ash bulb socket means fastened to said cover means, having an upper end portion, said ash bulb being mounted in the socket means, an insulating ring surrounding said socket means near its upper end, rst electrical contact means mounted on said ring, said contact means being conductively connected with the socket means, second electrical contact means adapted for contact with said first contact means only when the cover means is in ametight sealing position, a flash bulb ring circuit mounted in said housing comprising a capacitance, a charging circuit comprising a voltage source in series with the capacitance, a discharging circuit for said capacitance including a firing switch, means including said first and second electrical contact means for electrically connecting said flash bulb to said discharge circuit whereby said liash bulb ignites when the discharge circuit is completed by the firing switch, a resistance adapted to 4dissipate the energy in said capacitance, and third contact means in circuit for shunting the resistance across the capacitance when the cover means is retracted from its ametight sealing position.

2. An explosion-proof photollash unit comprising a photoash bulb having the usual threaded base portion and electrical terminals, a flametight housing surrounding said flash bulb including transparent window means, an access tube having inner and outer end portions connected to said housing at said inner end, retractable cover means mounted in said access tube adapted to form a flametight seal, flash bulb socket means mounted on said cover means having an upper end portion, said liash bulb being mounted in the socket means, an insulating ring surrounding said socket means near its upper end, electrical contact means mounted on said ring, said contact means being conductively connected with the socket means, switch means mounted in said housing, said switch means including a conducting actuating arm movable between a switch open and a switch closed position, said actuating arm contacting said electrical contact means only when in switch open position and the cover is in ametight closed position, a ash bulb tiring circuit mounted in said housing comprising a capacitance, a charging circuit comprising a voltage source in series with the capacitance, a discharging circuit for said capacitance including a :firing switch, means including the conducting switch actuating arm and ring electrical contact means for electrically connecting said ash bulb to said discharge circuit whereby said ash bulb ignites when the discharge circuit is completed by the ring switch, a resistance adapted to ldissipate the energy in said capacitance, contact means connected with the said switch means for shunting said resistance across the capacitance when the actuating arm is in switch closed position.

3. An explosion-proof photoiash unit comprising a photoflash bulb having the usual threaded base portion and electrical terminals, a ametight housing surrounding said ilash bulb including transparent Window means, an internally threaded access tube having inner and outer end portions, said access tube being integrally joined to said casing `at its inner end, a cover means threadedly mounted in said access tube, a shoulder portion on said cover means adapted to bear against the exterior end of the access tube and form a ametight seal, ash bulb socket means mounted on said cover means having an upper end portion, the said flash bulb being mounted in said socket means, an insulating ring surrounding the socket means at the upper end thereof and detachably connected therewith, a pair of circumferentially spaced electrical contacts mounted on said ring conductively connected to the ash bulb terminals, a pair of switches mounted in said housing, each having conducting actuating arms movable between a switch open and a switch closed position, and adapted to contact said insulating ring, whereby unscrewing the cover means moves the ring axially and causes movement of the switch actuating arm, said arm contacting the n'ng electrical contacts only when the cover is in closed ametight position, a llash bulb ring circuit mounted in said housing comprising a capacitance, a charging circuit comprising a voltage source in series with the capacitance, a discharging circuit `for said capacitance including a ring switch, means including the conducting switch actuating arms and ring electrical contacts for electrically connecting said ash to said discharge circuit whereby said ash bulb ignited when the discharge circuit is completed by the ring switch, a resistance adapted to dissipate the energy in said capacitance, contact means connected with said switches (for shunting said resistance across the capacitance when the actuating switch arms are in switch closed position.

4. An explosion-proof photoash unit comprising a photoash bulb having a base portion and electrical terminals, a ametight housing surrounding said flash bulb including transparent window means, an access tube having inner and outer end portions connected to said housing at said inner end, retractable cover means mounted in said access tube adapted to form a ametight seal, ash bulb socket means fastened to said cover means having an upper end portion, said flash bulb being mounted in the socket means, an insulating ring surrounding said socket means near its upper end, rst electrical contact means mounted on said ring, said contact means being conductively connected with the socket means, second electrical contact means adapted for contact with said first contact means only when the cover means is in ilametight sealing position, a flash bulb tiring circuit mounted in said housing comprising a capacitance, a charging circuit comprising a voltage source in series with said capacitance, a discharging circuit for said capacitance comprising a Thyratron tube connected in series to said capacitance, means connecting said ash bulb in said discharging circuit, means in circuit with the control grid of the Thyratron tube lfor causing said, tube to tire, whereby said capacitance discharges and ignites the ash bulb, a resistance adapted to dissipate the energy in said capacitance, and third contact means in circuit for shunting the resistance across the capacitance when the cover means is retracted from the flametight sealing position.

5. An explosion-proof photoash unit comprising a photoash bulb having a base portion and electrical terminals, a arnetight housing surrounding said ilash bulb includingtransparent window means, an access tube having inner and outer end portions connected to said housing at said inner end, retractable cover means mounted in said access tube adapted to form a ametight seal, flash bulb socket means `fastened to said cover means and having an upper end portion, said ilash bulb being mounted in the socket means, an insulating ring surrounding said socket means near its upper end, first electrical contact means mounted on said ring, said contact means being conductively connected with the socket means, second electrical contact means adapted for contact with said rst contact means only when the cover means is in ametight sealing position, a ash bulb iiring circuit comprising a capacitance, a charging circuit for said capacitance including a voltage source in series with the capacitance, a discharging circuit for said capacitance comprising a Thyratron tube connected in series to the capacitance, means connecting said ash bulb in series with said discharging circuit, a light sensitive photoelectric cell in circuit with the control grid of the Thyratron tube for causing said tube to re, whereby said capacitance discharges when the photoelectric cell is energized and ignites the flash bulb, a resistance adapted to dissipate the energy in said capacitance, and third contact means in circuit for shunting the resistance across the capacitance when the cover means is retracted from its flametight sealing position.

References Cited in the le of this patent UNITED STATES PATENTS 2,295,339 Ericson Sept. 8, 1942 2,304,085 Grilin Dec. 8, 1942 2,508,242 Stein May 16, 1950 2,546,734 Farber Mar. 27, 1951 2,624,831 Farber Jan. 6, 1953 2,757,317 Harlan July 31, 1956 2,763,812 McKinney et al Sept. 18, 1956 2,786,936 Appleton Mar. 26, 1957 2,840,690 Harling June 24, 1958 

